In recent years, in satellite communications, radars, etc., the need for formation of multiple beams and for reduction in the sidelobes of the antenna pattern has been increasing. Beam forming methodologies that satisfy this need includes a DBF, which is a beam forming methodology that uses digital signal processing. The DBF includes analog circuits, such as filters, amplifiers, down converters and AD converters (ADCs: Analog to Digital Converters), the number of analog circuits being equal to the number of element antennas (the number of systems). Then, the DBF multiples digitized signals of the element antennas by an excitation coefficient, and, after that, combines the digitized signals to form a beam. Because this DBF forms a beam by performing digital signal processing, the DBF can easily carry out formation of multiple beams and high-accuracy control of the antenna pattern.
A problem is, however, that the above-mentioned DBF have to include a plurality of analog circuits whose number is equal to the number of systems. Especially, the power consumption of each ADC is relatively higher than those of the other analog circuits, and its cost is also higher than those of the other analog circuits. Therefore, a problem with an antenna device using DBF is that its cost and its power consumption are high.
As a method of implementing DBF at a low cost and with low power consumption, there is, for example, an adaptive array antenna device described in Patent Literature 1. This adaptive array antenna device includes switches provided respectively for a plurality of element antennas, and switches on and off the switches in such a way as to receive a received signal of each of the element antennas in a time-division manner. Because this adaptive array antenna device simply has a single system of analog circuits, the number of ADCs which is a key factor of the cost and the power consumption can be reduced to one.